Just when you thought you had a grip on the basics of genetics, the GMF had to make it tough and assign you to this case.  In this case you will be dealing with the sometimes tricky situation of codominance of alleles in blood groups.  There are four different blood groups (A, B, AB, and O).  The letters of these blood groups refer to two carbohydrates which can be found on the red blood cells.  If a person has red blood cells coated with carbohydrate A, their blood is classified in blood group A.  If they have carbohydrate B coating their red blood cells, they are classified in blood group B.  If both carbohydrates are found, the blood is in group AB, and if neither carbohydrate is found, they are in blood group O.  These blood groups result from the combination of three different alleles, symbolized as I^A (punnet symbol Ia) for the A carbohydrate, I^B (punnet symbol Ib) for the B carbohydrate, and i (punnet symbol i) for neither carbohydrate.  The I^A and I^B alleles are both dominant to the i allele.

So, a person with a genotype of I^AI ^A or I^A I would have type A blood, I^BI ^B or I^B i would be type B, and  ii would be blood type O.  When combined, the alleles I^A and I^B are codominant (both are expressed in the phenotype), resulting in a genotype of I^AI^B which would be type AB blood coated with both types of carbohydrates.

In humans, when a male mates with a female, the genes for blood type are transferred as normal.  For example, a male with homozygous blood type A (I ^AI^A) would produce gametes I^A and I^A that would combine with the gametes I^B and i from a woman with heterozygous blood type B (I^B i).  The offspring would then be composed of 50% blood type AB (I ^AI^B), and 50% blood type A (I^A i) in this case.  The probability of producing offspring with different blood types would vary with the different parents (i.e. parents with blood types AB and O would have much different percentages and offspring).

Here's the scenario of this mission:

In late May of this year, two married couples, the Joads and the Caulfields, gave birth to baby boys at the Abruzzi Memorial Hospital in Italy.  While they were recovering, the attendants in the nursery room with their babies were making the final checks and preparing to go home for the night.  While she was collecting the charts from each of the baby's beds, the head nurse on staff accidentally bumped into a co-worker, spilling all of the information onto the floor.  The nurse, who claims she has a photographic memory, rearranged the paperwork in what she thought was the correct order.  The next day, when the two couples went to get their babies, they suspected that their babies had been switched.  The nurse assured them, however, that the babies they had were the correct ones.  The parents were still not convinced and commissioned the GMF to investigate.

Leslie Joad		Chad Joad		Cara Caulfield		Rick Caulfield

Baby #1		Baby #2

You will be equipped with the usual tools:

• The Punnet Calculator
• Your notebook
• Special hints

You will rendezvous with the couples in Italy as soon as you accept this mission.  Good luck and arivederci.